PURPOSE: The purpose of this study is to evaluate the safety and efficacy of orally administered voglibose (AO-128) in patients with type II diabetes mellitus for 52 weeks. Long term safety and tolerability are of primary interest in this study. Safety and tolerability will be evaluated by tabulating adverse experiences (clinical and laboratory data) and reasons for study discontinuation. Of secondary interest, the efficacy of AO-128 will be evaluated using changes in glycosylated hemoglobin (HbA1c). Type II diabetes is characterized by fasting hyperglycemia and glucose intolerance, manifested by a steep increase in post-prandial blood glucose concentration and insulin secretion. The goal in treatment of type II diabetes is to achieve normoglycemia, usually through use of diet and exercise therapy or with oral agents such as sulfonylureas (e.g., glipizide), biguanides (metformin), and, most recently, alpha-glucosidase inhibitors (acarbose). Voglibose, an N-substituted derivative of valiolamine, is an alpha-glucosidase inhibitor. The compounds in this class delay digestion of disaccharides and complex carbohydrates by reversible inhibition of alpha-glucosidases in the brush border of the small intestine. The inhibitory activity of voglibose is about 190-270 times more potent than acarbose, which has already received FDA approval. Because it favors inhibition of maltase and sucrase, voglibose is considered to be a selective disaccharidase inhibitor.